Starts tomorrow (or now if you're a member of their rewards scheme) with single advance tickets between Edinburgh and London for £10 in standard and £30 in first (each way).
Might be useful for someone who can travel on a certain train and wants to cheaply get to London fror a flight or work etc.

T&Cs:
For travel on East Coast trains only, from 7 January 2013 to 1 March 2013, excluding 15 - 24 February inclusive. Book by midnight 18 December 2012 only at eastcoast.co.uk/sale3. 40,000 £30 fares and 85,000 £10 fares will be made available for the offer and are subject to availability. Fares available across our route between London & Leeds, and London & Edinburgh and all calling points in between with the exception of Lincoln, Selby, Brough, Hull, Bradford, Shipley, Keighley, Horsforth, Skipton and Harrogate. Availability may be limited on Fridays and Sundays and for peak services. No other offers or discounts can be applied, including Railcards or child discounts. Travel on booked train only. No changes, no refunds and no break of journey permitted.